linux-kernel - Re: [PATCH] mm: add a new command-line kmemcheck value

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Message-ID: <52DF1D59.8090803@huawei.com>
Date:	Wed, 22 Jan 2014 09:22:33 +0800
From:	Xishi Qiu <qiuxishi@...wei.com>
To:	Vegard Nossum <vegard.nossum@...il.com>
CC:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	"Vegard Nossum" <vegardno@....uio.no>,
	Pekka Enberg <penberg@...nel.org>,
	Mel Gorman <mgorman@...e.de>, <wangnan0@...wei.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH] mm: add a new command-line kmemcheck value

On 2014/1/11 0:02, Vegard Nossum wrote:

> On 2 January 2014 02:34, Xishi Qiu <qiuxishi@...wei.com> wrote:
>> On 2013/12/31 18:12, Vegard Nossum wrote:
>>> On 31 December 2013 09:32, Xishi Qiu <qiuxishi@...wei.com> wrote:
>>>> Add a new command-line kmemcheck value: kmemcheck=3 (disable the feature),
>>>> this is the same effect as CONFIG_KMEMCHECK disabled.
>>>> After doing this, we can enable/disable kmemcheck feature in one vmlinux.
>>>
>>> Could you please explain what exactly the difference is between the
>>> existing kmemcheck=0 parameter and the new kmemcheck=3?
>>
>> kmemcheck=0: enable kmemcheck feature, but don't check the memory.
>>         and the OS use only one cpu.(setup_max_cpus = 1)
>> kmemcheck=3: disable kmemcheck feature.
>>         this is the same effect as CONFIG_KMEMCHECK disabled.
>>         OS will use cpus as many as possible.
>>
> 
> I see. In that case, I think it's better to allow all the CPUs to keep
> running while kmemcheck is disabled with kmemcheck=0 boot parameter,
> and offline them when/if kmemcheck is reenabled via
> /proc/sys/kernel/kmemcheck.
> 
> 
> Vegard
> 
> 

Hi Vegard,

In some scenes, user want to check memory dynamicly, this "dynamically" 
means we can turn on/off the feature at boottime, not runtime. Without 
this patch, if user want to use this feature, he should change config 
and build the kernel, then reboot. This is impossilbe if user has no 
kernel code or he don't know how to build the kernel.

boottime: kmemcheck=0/1/2/3 (command-line)
runtime: kmemcheck=0/1/2 (/proc/sys/kernel/kmemcheck)

The main different between kmemcheck=0 and 3 is the used memory. Kmemcheck 
will use about twice as much memory as normal.

Thanks,
Xishi Qiu

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